Behrmann, Jan Hinrich

Völker, David

Weinrebe, Reimer Wilhelm

English

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Geophysical Research Abstracts,Vol. 10, EGU2008-A-03854, 2008SRef-ID: 1607-7962/gra/EGU2008-A-03854EGU General Assembly 2008© Author(s) 2008Mass wasting-related Morphology of the SouthernCentral Chilean continental Margin - quantitativeComparison with other active MarginsD. Völker (1), W. Weinrebe (1), J. Behrmann (1)Leibniz-Institut für Meereswissenschaften an der Universität Kiel (IFM-GEOMAR),Wischhofstr. 1-3, 24148 Kiel, Germany; email: dvoelker@ifm-geomar.deOffshore Southern Central Chile (35-42˚S) large segments of the lower continentalslope are shaped by mass-wasting events. The quantitative assessment of these fea-tures allows the comparison with well-studied cases elsewhere in terms of rheology,process dynamics and - ultimately - their implication for the tsunami hazard of theChilean coasts. The cases to compare with are the continental margin of Oregon andthe Pacific margin of Central America (Nicaragua and Costa Rica). Offshore Oregon,mass wasting events are visible as detached blocks which lie on top of the trench fill,have some 50-100 km2 areal extent, maintain a part of their post-failure cohesion andproduce high and steep headscarps. This particular segment of the margin is knownfor having produced historic tsunamis. An Olistolith, similar in size and morphologi-cal aspects is observed offshore central Chile.Offshore central Costa Rica, the front of the margin wedge is heavily indented as aconsequence of mass removal due to the interaction of the lower slope with seamountswhich were formed at the Galapagos Hotspot are subducted along with the Co-cos Plate. The resulting indentations resemble in size and their morphological ap-pearence some large (600 km2) amphitheatre-shaped depressions which we see inswath bathymetry data of the middle slope of central Chile. Offshore Nicaragua,frontal oversteepening due to continuous frontal erosion leads to the formation of nor-mal faults and mass wasting on the middle slope.The Southern Central Chilean case is interesting because it represents a transition be-tween a past erosional and a present accretionary phase. Today the trench is filledby sediments and frontal accretion as well as sediment subduction seem to be theprevalent processes which shape the lowermost slope, but a number of morphologi-cal features indicate oversteepening and extension, so some of the structures may beinherited from the erosional past.

Mass wasting-related morphology of the Southern Central Chilean continental margin - quantitative comparison with other active margins

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